The Flow Cytometry Core at MSKCC provides researchers at MSKCC with state of the art flow cytometry services, including cell sorting. These services include operator-assisted flow cytometry analysis on a CyAn and a FACSCaliburflow cytometer, self-operated flow analysis on two 5-color (upgraded) FACScans and a FACSCalibur, and operator-assisted cell sorting on one 4-laser MoFlo, one 3-laser MoFlo, and one 3-laser DiVa cell sorter. Extensive training in flow cytometry is offered, and a site license for Flowjo is administered by the core facility. An additional cell purification option, Miltenyi AutoMACS, is made available to all users. The availability of these services enables the researchers at MSKCC to isolate and characterize specific cellular subsets, and to analyze the effects of manipulations aimed at answering a multitude of scientific questions that arise within the context of cancer research. The core facility's services play in important role in enabling the researchers to ask specific questions regarding ever smaller subsets of cells, down to the single cell level. Many of these questions can only be answered when purified fractions of specific cell subsets can be identified and isolated, which is the domain of flow analysis and cell sorting.